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Astro 10-Lecture 1: Introductions Who am I? Dr. Eric Korpela korpela@ssl.berkeley.edu http://setiathome.ssl.berkeley.edu/~korpela/ (510) 643-6538

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Course Goals To give you an understanding of what science is, how it works, and what it can and can’t tell us. To give you an appreciation of the night sky To make you excited about and interested in astronomy To allow you to critically assess popular portrayals of astronomy

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A promise and a warning The promise: –You will learn a lot. The warning: –Each lecture builds on material from earlier lectures, so it’s easy to fall behind and hard to catch up again.

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Expected Work-load Expect to put in 2-3 hours outside class for each hour of lecture. (6-9 hours per week) –Read the assigned material before coming to class. –Homework will be assigned every 2-3 weeks. Homework is accepted up to 1 week late for half credit Homework will not be accepted after solutions are available. –There will be 2-3 projects assigned during the semester The will be handed out a long time before they are due. DON’T WAIT UNTIL THE LAST MINUTE TO DO THEM!

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Exercises, Quizzes and Exams There will be an in class exercise or a quiz each week as a means of taking attendance. –If you arrive late and miss a quiz, be sure to let me know you attended class. There will be 3 exams. –In class, one hour followed by a guest lecture. –Final is non-cumulative. –Let me know at least 2 weeks in advance if you have a conflict.

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Grading Grading is on a curve. Breakdown Homework 20% Exercises and Quizzes15% Projects 20% Exams45%

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What is Astronomy? Literally: aster = star + nomie=naming (Astrology was already taken) Astronomy, in modern terms, is observational scientific study of the universe and its contents. Astrophysics is the combination of astronomy with theoretical understanding of the processes taking place in astronomical objects.

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A more basic question: What is science? Is science a collection of facts? No! Science is a process. It’s a means by which we try to understand how the world works. Example: Watch a football game. Try to figure out the rules without knowing them or having a rule book. Science is the process of trying to create a universal rule book.

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A gallery of the skies

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A review of scientific notation. Astronomy deals with very large and very small numbers… Distance from Earth to Sun ~ 150 000 000 000 meters Mass of hydrogen atom ~ 0.000 000 000 000 000 000 000 000 001 67 kg 1.5x10 11 meters 1.67x10 -27 kg

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A review of scientific notation. Significant figures… (Number of digits before the ‘x’) 2 significant figures 3 significant figures 1.5x10 11 meters 1.67x10 -27 kg

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How far does light travel in 65.1 millionths of a second? d=v x t = 3.0x10 8 m/s x 6.51x10 -5 s Multiply the mantissas (the numbers before the ‘x’) 19.53 x 10 8 x 10 -5 m/s s Add the exponents (the numbers above the 10) 19.53 x 10 3 m/s s Shift the decimal to the first place by adding or subtracting from the exponent. 1.953 x 10 4 m/s s Round to the minimum number of significant digits in the original numbers. 2.0 x 10 4 m/s s Cancel units to get the correct units 2.0 x 10 4 m = 20,000 meters = 12 miles

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How long does it take light to get from the Sun to the Earth? t = d/v = 1.5x10 11 m / 3.0x10 8 m/s Divide the mantissas (the numbers before the ‘x’) 0.5 x 10 11 / 10 8 m / (m/s) Subtract the exponents (the numbers above the 10) 0.5 x 10 3 m/(m/s) Shift the decimal to the first place by adding or subtracting from the exponent. 5 x 10 2 m/(m/s) Round to the minimum number of significant digits in the original numbers. 5.0 x 10 2 m/(m/s) Cancel units to get the correct units 5.0 x 10 2 s = 500 s = 8.3 minutes

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How fast are you moving right now? Rotation of the Earth radius of the earth = R e = 6400 km = 6.4x10 3 km 1 day = 86400 seconds = 8.64x10 4 sec v = d/t = 2 R e /1 day = 4.0x10 4 km/day / 8.64x10 4 s/day = 4.6x10 -1 km/s ~ 1000 mph

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How fast are you moving right now? Orbit of the Earth around the Sun radius of the earth’s orbit = A.U. = 1.5x10 8 km 1 year = 3.16x10 7 sec v = d/t = 2 A.U./year = 9.4x10 8 km/day / 3.16x10 7 s/day = 30 km/s ~ 67 000 mph

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How fast are you moving right now? Orbit of the Sun around the Galaxy 200 km/s ~ 450 000 mph Movement of Galaxy with respect to the rest of the universe 540 km/s ~ 1.2x10 6 mph

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A reminder: The metric system Basic units: meter (m), gram (g), second(s) Prefixes Giga (G)10 9 Mega (M)10 6 kilo (k)10 3 hecto (h)10 2 centi (c)10 -2 mili (m)10 -3 micro ( ) 10 -6 nano (n) 10 -9

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Other units used in Astronomy Astronomical Unit (AU) = distance from Earth to the Sun = 1.5x10 11 m Light Year (ly) = distance light travels in one year = d = v t = 3.0x10 8 m/s x 3.16x10 7 s = 9.5x10 15 m Parsec (pc) = 206264.81 AU = 3.26 ly = 3.1x10 16 m

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The scale of the universe How can we understand these distances on a human scale? The sun is 1.5x10 11 m away. A passenger jet travels at 600 mph ~ 270 m/s If you could fly to the sun, the trip would take… t = d/v = 1.5x10 11 m / 270 m/s =5.6x10 8 s = 18 years! The next nearest star is 4.3 light-years away, 270 000 times as far. It would take 4.8 million years to get there by jet!

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The scale of the universe Powers of Ten [video]

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SCALE MODELS Scale of the Solar System

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Solar System

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Relative Size of Earth and Moon

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Relative Sizes of Planets

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Distances Between Planets

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SCALE MODELS A scale model of the history of the universe

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A scale model of history The universe is about 13 billion years old. To make it a bit more comprehensible scale it to 1 day.

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A scale model of history 12:00 am 0 secondsThe Big Bang! 12:00:03 400 kyThe universe becomes transparent 12:22200 MyThe first stars form 1:501 GyMilkyway Galaxy forms 3:41 pm8.5 GySolar System forms 4:03 8.7 GyEarliest indications of life on Earth 7:239.5 GyContinents begin to form 8:522.5 GyaEarliest multicellular life forms 10:46 670 MyaFirst land plants 11:00530 MyaFirst insects 11:13430 MyaFirst fish 11:35230 MyaDinosaurs evolve 11:5365 MyaDinosaurs die out

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A scale model of history 11:59:265 MyaFirst apes that walk erect (homonoids) 11:59:59.33 100 kyaModern humans appear 11:59:59.93 10 kyaAgriculture developed 11:59:59.975 kyaGreat pyramids built 11:59:59.9987 204 yaAmerican Revolution 11:59:59.99989 18 yaAbout when most of you were born.

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How does science work? A scientist makes an educated guess about a rule: a hypothesis. –A hypothesis needs to be quantitative. –It needs to make predictions about the behavior of the universe. –A hypothesis builds on existing knowledge of the universe The hypothesis is tested by experiment or observation. –If the hypothesis fails a test it must be discarded or modified. Example Hypothesis: All objects fall when dropped…. –Is this hypothesis true or false? A hypothesis that never fails despite repeated tests of its predictions is called a theory. (In science, ‘a theory’ is something that is a near certainty.)

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How does science work? Science isn’t about ‘truth.’ It’s about what has worked so far. –No hypothesis can be proven to be true. It can only be shown to be false. (A hypothesis must be falsifiable.) –A complete hypothesis must work at all places and times. –Only one bad prediction is required to falsify a hypothesis. Example: Newton’s Law of Universal Gravitation –superceded by Einstein’s Theory of General Relativity –still a useful approximation for most situations despite having been falsified.

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Things that are not science... Astrology - It makes predictions, but the theory/method isn’t changed when predictions fail Creation Science - It makes no testable predictions. Not falsifiable. Psychic precognition - theory/method isn’t changed when predictions fail. Religion - Not falsifiable. ’Not science’ does not mean ‘not true’ any more than ‘science’ means ‘truth.’

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How would a scientist find the answer the following questions? How long does it take to cook a turkey? Why does it take that long to cook a turkey? The difference between these questions is the difference between observational fact and science.

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